FR3044239A1 - ANTI-UV EMULSIONS STABILIZED WITH LIGNIN AND NANOPARTICLES - Google Patents

Abstract

The present invention relates to an "oil-in-water" type emulsion comprising an aqueous phase, a fatty phase, and an adsorption layer at the interface of the two phases, said adsorption layer consisting of a matrix of lignin in which are incorporated metal oxide nanoparticles, characterized in that the lignin is present in an amount of less than 2% by weight, and that the metal oxide nanoparticles are present in an amount of less than 1.5% by weight, relative to the total weight of the emulsion.

Description

The present invention relates to emulsions, and more specifically to "oil-in-water" type emulsions comprising an adsorption layer between the two phases having ultraviolet anti-oxidant and anti-radiation properties.

INTRODUCTION

Emulsions are widely produced and used in industry as either materials to be consumed or to be applied to surfaces as carriers of non-water soluble agents. We find emulsions in pharmacy, in cosmetics (milks, creams, ointments), in cooking (sauces, creams), in painting, in the road industry, in agrochemistry, in detergency, in rolling mills, in the iron and steel industry, and in manufacturing. various deposits (printing, adhesives ...).

In cosmetics and pharmacy, emulsions are an effective way to obtain a harmonious combination of ingredients of different nature and properties, including lipophilic and hydrophilic ingredients, in a homogeneous and easy-to-use presentation.

An emulsion can be defined as an intimate mixture of two immiscible liquid substances, consisting of an aqueous phase and an oily or oily phase. By mechanical and / or chemical action, the creation of an emulsion makes it possible to mix these two phases, one of the phases being dispersed in the second in the form of small droplets.

There are emulsions of the type "oil in water" and "water in oil". Thus, an oil-in-water emulsion (O / W or O / W for oil in water) is composed of an oily phase dispersed in an aqueous phase. This is a "direct" emulsion. Conversely, a water-in-oil emulsion (W / O or W / O for water in oil) is composed of an aqueous phase dispersed in an oily phase. A W / O emulsion is more greasy to the touch, because the touch corresponds mainly to the nature of the external phase. Such an emulsion is called "inverse". From a thermodynamic point of view, emulsions are inherently unstable, especially over time. The mixture remains stable thanks to the presence of an ingredient called emulsifier or emulsifier.

Emulsifiers are most often surfactants or surfactants. The emulsifiers may be ionic or nonionic in nature. The molecules used may be of natural or synthetic origin.

Some emulsifiers have specific advantages, additional to their stabilizing properties. Thus, certain emulsifiers protect the active ingredients against oxidation, against ultraviolet rays, and / or their preservation within emulsions. These emulsifiers, which make it possible to protect the lipophilic active principles contained in the fatty phase, are actively sought. Indeed, the oxidative stability of the active molecules in emulsions is a particularly important point in the cosmetics industry.

Free radicals such as hydroxyls, peroxyls and superoxyls are triggers for oxidation of the active molecules. These radicals are generated either in the aqueous phase or at the oil / water interface of the emulsions, under the effect of various external parameters such as light and oxygen. These free radicals can pass through the adsorption layer, and thus initiate oxidative reactions of the products encapsulated in the lipid phase. This oxidation phenomenon is accelerated in the presence of UV rays.

Among the products sensitive to oxidation, mention may be made of vegetable oils, which often constitute a good portion of the fatty phase of the cosmetic compositions. When the oils are oxidized, they have a rancid odor and a color change. We can also mention vitamins, which can be degraded following a more or less long exposure to ultraviolet rays.

Thus, emulsions containing fragile lipophilic active principles, in particular those that are degraded / oxidized when exposed to light for too long, must be kept in opaque containers or in smoked glass, and preferably in total darkness, in order to preserve their properties. qualities over time.

This generates a real cost for the manufacturer who must use suitable containers, and is a disadvantage for the user, who must maintain the emulsion under appropriate conditions to maintain the qualities of the active ingredients and oils present in said emulsion.

In order to overcome this need to use an appropriate container, compounds with protective properties against oxidation and damage caused by ultraviolet (UV) radiation have been identified and integrated into the adsorption layers. found at the interface of aqueous and fatty phases.

Indeed, the structure of the adsorption layer can very significantly reduce the occurrence of oxidation reactions, by limiting the interactions of the products encapsulated in the lipid phase with free radicals and oxygen present in the aqueous phase. and / or absorbing or dispersing ultraviolet rays.

Thus, this adsorption layer may consist of compounds having antioxidant capacities and clean UV filters, and / or comprise compounds having an ability to potentiate the effects of other active compounds, thus protecting the lipophilic compounds against oxidation and damage caused by ultraviolet rays.

Among the compounds known for their properties of UV filters, mention may be made of metal oxide nanoparticles, conventionally used in cosmetic compositions intended for sun protection. The nanoparticles of metal oxide and their use as photoprotective agents are known and described, for example, in the patent applications EP 518772 and EP 518773. These nanoparticles make it possible to protect the materials with which they are associated with visible radiation and ultraviolet radiation. absorbing radiation in the wavelength range from 250 nm to 400 nm.

One can also mention lignin, a natural polymer capable of absorbing ultraviolet rays. It has recently been shown that lignin can advantageously be incorporated into UV absorber films, also comprising cellulose nanocrystals (WO 2012/156652). Lignin also has antioxidant properties (Pouteau et al., 2003). In addition, lignin acts as an emulsifier for stabilizing emulsions (Rojas et al., 2007).

The patent application US 2002/0182155 describes compositions comprising a combination of particulate fillers (clay for example) and lignin, which makes it possible to potentiate the effectiveness of compounds capable of absorbing UV radiation, such as nanoparticles of carbon dioxide. titanium (TiOi). Large amounts of titanium dioxide and / or lignin are used in these compositions to achieve a satisfactory Sun Protection Factor (SPF).

The problem to be solved by the present invention is to reduce, in emulsions, the amounts of lignin used and especially of metal oxide nanoparticles, while maintaining sufficient protection against the harmful effects of UV radiation and free radicals.

Indeed, various studies have highlighted the fact that nanoparticles of titanium dioxide and zinc monoxide, used in cosmetics and in particular in sun creams, are potentially toxic. At present, the potential adverse effects of these compounds are actively sought by scientists (Shi et al., 2013) and (AFSSAPS report on nanomaterials in cosmetics, adopted on 15/03/2011) . Nevertheless, there are no compounds with similar UV absorbance capabilities; thus, the research is directed towards the determination of particular conditions which make it possible to reduce the doses used of nanoparticles of metal oxide, while maintaining an effective absorbance of the UV rays.

SUMMARY OF THE INVENTION

The present invention relates to an emulsion of the "oil-in-water" type, comprising an adsorption layer allowing both the stability of the emulsion, and the protection of the lipophilic active principles against UV radiation and against agents. oxidation.

Said adsorption layer consists of a lignin matrix, comprising nanoparticles of metal oxide, in particular proportions, making it possible to optimize the antioxidant and anti-UV properties of this adsorption layer while minimizing the quantities used of the constituents of this adsorption layer.

More particularly, the present invention relates to an "oil-in-water" type emulsion comprising an aqueous phase, a fatty phase, and an adsorption layer at the interface of the two phases, said adsorption layer consisting of a lignin matrix in which are incorporated metal oxide nanoparticles, characterized in that the lignin is present in an amount of less than 2% by weight, and that the metal oxide nanoparticles are present in an amount of less than 1.5% by weight, based on the total weight of the emulsion.

The present invention relates to the improvement of the properties of this adsorption layer composed of lignin, by incorporation into the lignin matrix of nanoparticles of metal oxide, this incorporation making it possible in particular to improve: the rheological properties of said layer of adsorption; and the capacity of the metal oxide nanoparticles to absorb UV rays, and thus the possibility of reducing their quantity.

FIGURES

Figure 1. UV absorbance of the lignin molecule alone. The different wavelengths are presented on the abscissa axis, the intensity of the absorbance capacity of the lignin molecule is indicated on the ordinate axis.

Figure 2. UV absorbance of the lignin molecule in aqueous solution, alone or in the presence of different metal oxide nanoparticles: T1O2 (Eusolex T2000, Eusolex T S, organosolve) and ZnO.

Figure 3. Lignin adsorption kinetics at the fatty phase / aqueous phase interface: effects of the presence of metal oxide nanoparticles on the surface tension (mN / m), as a function of time, shown in FIG. axis of the adscisses.

Figure 4. Sun protection factor (SPF) and UVA protection factor (FP-UVA) obtained as a function of the concentration of T1O2 nanoparticles (represented on the abscissa axis), in the presence of 1.2% of lignin.

DETAILED DESCRIPTION

The present invention relates to an "oil-in-water" type emulsion comprising an aqueous phase, a fatty phase, and an adsorption layer at the interface of the two phases, said adsorption layer consisting of a matrix of lignin in which are incorporated metal oxide nanoparticles, characterized in that the lignin is present in an amount of less than 2% by weight, and that said nanoparticles are present in an amount of less than 1.5% by weight, relative to the weight total emulsion.

As indicated above, an emulsion is a dispersion, in the form of droplets, of two liquids immiscible with each other. It consists of an aqueous phase and a fatty phase. An oil-in-water type emulsion is characterized in that the fatty phase is dispersed, in the form of droplets, in the aqueous phase.

For the purposes of the invention, the term "aqueous phase" is understood to mean the phase which comprises water and / or at least one water-soluble solvent, ie a compound which is liquid at ambient temperature and is miscible with water. The aqueous phase may also comprise any water-soluble or water-dispersible compound compatible with an aqueous phase such as gelling agents, film-forming polymers, thickeners, surfactants and mixtures thereof.

For the purposes of the invention, the term "fatty phase" is understood to refer to the phase that includes any liquid fatty substance, generally an oil or a hydrocarbon. This phase may also be referred to as an oily, organic or lipophilic phase, these adjectives being used interchangeably and designating the same phase in the present application.

Within the meaning of the invention, the term "adsorption layer" designates the layer forming at the aqueous phase / fat phase interface in the emulsion, and making it possible to maintain the stability of the dispersion of the oil droplets in the aqueous phase.

"Ultraviolet filters" or "UV filters" means substances that absorb, reflect or disperse such radiation. For the purpose of the present invention, these substances are intended to protect the lipophilic products contained in the fatty phase of the emulsions.

For the purposes of the invention, the expression "lignin matrix" designates the three-dimensional lignin network that takes shape at the interface of the aqueous and fatty phases, and constitutes the "base" of the adsorption layer around the microdrops. oily phase.

Lignin

Lignin is one of the main components of wood, along with cellulose and hemicellulose. Its main functions are to provide rigidity, waterproofness and resistance to decomposition. All vascular plants, woody and herbaceous, produce lignin.

Lignin is the second most abundant renewable biopolymer on Earth after cellulose. This polymer consists of at least three different types of monomers, the following monolignols: coumaryl alcohol, called H unit (hydroxyphenyl), without methoxy group; coniferyl alcohol, referred to as G unit (guaiacyl), to a methoxy group; Sinapyl alcohol, called S-unit (syringyl), with two methoxy groups.

The fraction of each monomer varies considerably according to the plant line (gymnosperm, monocotyledonous angiosperm, dicotyledonous angiosperm); of the species; of the organ; fabric ; and in a general way of the physico-chemical environment in which the plant grows.

There is therefore no single and precise definition of lignin, because of its great variability and that within a given species.

Lignin is a polymer that adopts a three-dimensional network structure, also called a 'grid' or 'matrix', said network allowing interconnections between the adsorption layers present around each droplet of fatty phase. This matrix has very interesting mechanical properties, allowing both a very good stabilization of the emulsion and a good mechanical strength of the adsorption layer.

The lignin used in the emulsion according to the invention is preferably a lignin of natural origin.

Natural lignins are preferably extracted from woody or herbaceous vascular plants by performing acidolysis in an organic solvent. For example, the extraction mode in a dioxane / water medium, in the presence of hydrochloric acid, makes it possible to obtain lignin preparations that are relatively unmodified and low in associated sugars (Monties B, 1988).

According to a particular aspect of the invention, the lignin used in the emulsion according to the invention is derived from a process for extracting cellulose from plants.

According to another aspect of the invention, the lignin used in the emulsion according to the invention is of synthetic origin.

Lignin of synthetic origin, also called 'DHP' for 'dehydropolymer', can be synthesized in vitro in two stages: (i) synthesis of coniferyl alcohol or other monolignol and (ii) polymerization of monolignols in the presence of water oxygenated and peroxidase.

It is understood that the lignin used in the emulsion according to the invention can be purified or not, and may have been chemically modified. The emulsion according to the invention therefore comprises an adsorption layer consisting of a lignin matrix in which metal oxide nanoparticles are incorporated, in specific amounts.

Metal oxide nanoparticles

The metal oxide nanoparticles are used here as UV filters for absorbing, reflecting or dispersing UV radiation.

The metal of said metal oxide is advantageously selected from the group consisting of titanium, zinc, cerium, zirconium, iron, copper, and mixtures thereof, preferably from the group consisting of titanium, cerium, zinc , and their mixtures. Preferably the metal is titanium.

According to one embodiment, said metal oxide is selected from the group consisting of titanium dioxide (TiC> 2), zinc monoxide (ZnO), cerium oxides (Ce2C> 3 and CeCU), zirconium dioxide (ZrCh) and copper oxides (CuO and CU2O).

In a preferred aspect of the invention, the metal oxide nanoparticles are nanoparticles of zinc monoxide (ZnO) of CAS number 1314-13-2, or of titanium dioxide (TiO2) of CAS number 13463-67-7 these two types of nanoparticles can be incorporated into cosmetic compositions from a regulatory point of view.

Titanium dioxide nanoparticles are particularly preferred.

It is understood that these nanoparticles may be used as commercial products which may comprise up to 30% other agents or excipients. Advantageously, products with at least 70% metal oxide nanoparticles will be chosen. By way of information, various commercial compounds comprising nanoparticles that can be used in the emulsions of the invention are listed in the tables below:

Table 1

Table 2

Most preferably, the titanium dioxide nanoparticles used are selected from those of the brand Eusolex T-2000® and Eusolex T-S®, or a mixture of both.

According to another aspect of the invention, a mixture of at least two different types of metal oxide nanoparticles is used. It may in particular be used a mixture of nanoparticles of zinc monoxide and titanium dioxide.

By nanoparticles is meant nanoparticles having a mean diameter of between 2 nm and 100 nm, or between 2 nm and 50 nm, advantageously between 4 nm and 30 nm, preferably between 6 nm and 20 nm, more preferably between 8 nm. and 10 nm.

Nanoparticles of metal oxide with a mean diameter of less than 2 nm can be envisaged. However, when the average diameter is smaller than the pore size of the dermis, said nanoparticles can pass through the skin, which is not a preferred embodiment of the present invention.

The metal oxide nanoparticles are incorporated into the matrix created by the lignin polymer. Said nanoparticles are thus "integrated" or "trapped" in this polymer network. Any technique consisting of mixing and homogenizing the two compounds is suitable for the implementation of the invention. It is preferable to obtain a good uniformity of the particle distribution in the lignin matrix.

According to a first implementation of the invention, the metal oxide nanoparticles are bonded to the lignin matrix by non-covalent bonds. Said nanoparticles are incorporated in the lignin matrix and remain in place thanks to non-covalent bonds existing between these molecules. Thus, bonds for the assembly of molecules, such as hydrogen bonds, coordination

metallic, hydrophobic forces, van der Waals forces, stacks (π-π), electrostatic and electromagnetic interactions.

In a preferred aspect of the invention, the metal oxide nanoparticles are incorporated into the lignin matrix by sonication.

The technique of sonication is based on the use of 'sonicator' devices producing waves in the ultrasounds, which agitate the molecules and thus allow their homogenization.

According to a second embodiment of the invention, the metal oxide nanoparticles are bonded to the lignin matrix by covalent bonds. A covalent bond is a chemical bond in which two atoms share two electrons of one of their outer layers to form a pair of electrons bonding the two atoms.

A covalent interaction between these molecules can be obtained in particular when a chemical bond is established between the empty vacant orbital of the metal oxide, and the electronic doublet of oxygen, a very abundant atom in the lignin molecule. The incorporation of these nanoparticles within the lignin matrix makes it possible to optimize their capacity of LTV filters, and thus makes it possible to reduce the quantity of nanoparticles used while retaining satisfactory protection properties against UV rays.

Quantities and ratios considered according to the invention

The present invention relates to an emulsion comprising an adsorption layer consisting of a lignin matrix in which are incorporated metal oxide nanoparticles, characterized in that the lignin is present in an amount of less than 2% by weight, and that said nanoparticles are present in an amount of less than 1.5% by weight, based on the total weight of the emulsion.

As previously presented, it is indeed essential to reduce in the emulsions the amount of these "ancillary" compounds which are not active compounds, while maintaining their stabilizing properties of the emulsion and protecting the active compounds against UV rays and oxidizing agents.

A small amount of metal oxide nanoparticles in the emulsified system is preferable for all the reasons mentioned above; in addition, at high concentrations, it has been observed that the absorptive power of the metal oxide nanoparticles is attenuated.

In a first aspect, the lignin is present in the emulsion in an amount of less than or equal to 2% by weight, relative to the total weight of the emulsion. The lignin may especially be present in a quantity of 2, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, or 0.5% by weight, relative to the weight total emulsion.

In a second aspect, the metal oxide nanoparticles are present in the emulsion in an amount of less than or equal to 1.5% by weight, relative to the total weight of the emulsion. Said nanoparticles may in particular be present in an amount of 1.5, 1.4, 1.3, 1.2, 1.1, 1, 0.9, 0.8, 0.7, 0.6, or 0.5% by weight, relative to the total weight of the emulsion.

According to one aspect of the invention, in these emulsions, the weight ratio nanoparticles of metal oxide / lignin is less than 1.

More particularly, in these emulsions, the weight ratio nanoparticles of metal oxide / lignin is less than 1, less than 0.9, less than 0.8, less than 0.7, less than 0.6, less than 0.5, less than 0.4, less than 0.3, or less than 0.2.

According to a preferred aspect of the invention, the nanoparticles of metal oxide are present in a ratio by weight nanoparticles / lignin of between 0.1 and 0.8, and more preferably are present in a ratio by weight nanoparticles / lignin of about 0.5.

According to a particular aspect of the invention, the "oil-in-water" type emulsion consists of an aqueous phase, a fatty phase, and an adsorption layer at the interface of the two phases, said adsorption layer consisting of a lignin matrix in which metal oxide nanoparticles are incorporated, the emulsion not comprising a particulate thickener.

The term "particulate thickener" is understood to mean, in particular, thickeners such as smectite clays, which include montmorillonite, bentonite, bidelite, hectorite, saponite, stevensite, etc.

It is understood that, according to this implementation, the aqueous and fatty phases consist of different lipophilic compounds (in the fatty phase) and hydrophilic (in the aqueous phase) but do not include particulate thickener.

According to a particular aspect of the invention, the fatty phase may represent at least 50% by weight of the emulsion, relative to the total weight of the emulsion. Such an emulsion is referred to as a "concentrated emulsion".

In particular, the emulsion may comprise at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% by weight of fatty phase, relative to the total weight of the emulsion.

According to a preferred aspect of the invention, the fatty phase represents between 50 and 70% by weight of the emulsion.

The fatty phase of the emulsion according to the invention comprises at least one fatty substance chosen from fatty substances that are liquid at room temperature (20-25 ° C.), such as volatile or non-volatile oils of vegetable, mineral or synthetic origin. , and their mixtures. The fatty phase may also include any usual additive, liposoluble or lipodispersible.

For an application in the cosmetic field, these oils are chosen from physiologically acceptable oils.

As oils that can be used in the composition of the invention, mention may be made, for example: • hydrocarbon-based oils of animal origin; • hydrocarbon oils of vegetable origin; Esters and synthetic ethers, especially of fatty acids; • linear or branched hydrocarbons of mineral or synthetic origin, such as paraffin oils, volatile or not, and their derivatives; Partially fluorinated and / or silicone fluorinated oils; • silicone oils; • and their mixtures.

Among the hydrocarbons of formula CnHm, with n and m being two whole numbers, the linear, aromatic and cyclic hydrocarbons can be used, whatever their boiling point.

Essential oils, in particular extracted from plants, are preferred hydrocarbons for the implementation of the invention.

More particularly, as hydrocarbon which may be present in the fatty phase of the invention, mention may be made of cyclopentane (C 5 H 10), hexane (C 6 H 6), methylcyclohexane (C 7 H 14), heptane (C 7 H 16), decane (C 10 H 22), dodecane (C12H26) and toluene (¢ 7¾).

The fatty phase in the emulsion according to the invention may be composed of a single oil, in particular a single hydrocarbon, or may also consist of a mixture of two, three or even four different oils.

According to one aspect of the invention, the fatty phase comprises an organic solvent chosen from cyclopentane, hexane, methylcyclohexane, heptane, decane, dodecane and toluene.

According to another aspect of the invention, the fatty phase consists mainly or completely of an organic solvent selected from cyclopentane, hexane, methylcyclohexane, heptane, decane, dodecane and toluene.

The aqueous phase of the emulsion according to the invention mainly comprises water and optionally one or more compounds miscible with water. The aqueous phase may also include ionic species, pH regulators, and all the active, preservative and coloring ingredients that are water soluble or water dispersible.

EXAMPLES

The products used in this study are branded SIGMA-ALDRICH and are used without further purification: Decane> 95%

Lignin: Lignin, alkali low sulfonate content 471003 Aldrich

Nanoparticles of ZnO

TiO 2 nanoparticles: a) TiO 2 (organosolve W877). b) TiO 2 (Eusolex T-S®) c) TiO 2 (Eusolex T-2000®)

Example 1. Preparation of aqueous solutions of lignin and metal oxide nanoparticles

In order to verify the miscibility of these nanoparticles in a polymer matrix of lignin, we mixed them with the aqueous solution of lignin (0.1g lignin solubilized in 3.5 ml of water) by sonication according to the following conditions: for 7 minutes, 1 second 'up', 1 second 'off, amplitude 30%, at T ° = 25 ° C, with a Vibra cell 75115 sounder brand BIOBLOCK SCIENTIFIC.

After complete evaporation of the aqueous phase, scanning electron microscopy (SEM) images made it possible to observe that the nanoparticles of ZnO and TiC> 2 have a high affinity for lignin and that they "penetrate" perfectly into the matrix constituted by this natural polymer.

Example 2. Preparation of stabilized decane / water emulsions with lignin and metal oxide nonaparticles

The emulsions are prepared by stirring the oil and water phases in the presence of lignin by sonication as described above.

Concentrated emulsions composed of 6.5 decane / 3.5 water (v / v) are stabilized with 100 mg of lignin without nanoparticle (1), or with lignin supplemented with 50 mg ZnO (2), 50 mg TiO 2 W877 Organoslove (3), 50 mg TiO 2 (Eusolex TS) (4) or 50 mg TiO 2 (Eusolex T2000) (5).

After complete evaporation of the aqueous and organic phases of these emulsions, the adsorption layer of each of these emulsions was photographed. The scanning electron microscopic images of the adsorption layers make it possible to observe that the adsorption layer has a fairly regular porous structure.

EXAMPLE 3 UV Absorbance of the aqueous solutions of lignin in combination with different types of metal oxide nanoparticles

30 g / l aqueous solutions of lignin, with and without ZnO and TiO 2 nanoparticles, are prepared. All solutions are mixed by sonication for 7 minutes, with pulsations of 0.1 seconds' on ', 0.1 seconds' off.

Table 3

As shown in Figure 1, lignin alone significantly absorbs rays at the 280 nm wavelength.

FIG. 2 shows that in the presence of TiO 2 nanoparticles (Eusolex T2000), a significant increase in absorbance intensity of the lignin + nanoparticle combination is observed.

EXAMPLE 4 Lignin adsorption kinetics in combination with different types of metal oxide nanoparticles at the decane-water interface The main objective of this test is to study the effect of the presence of different nanoparticles ( TiO 2 and ZnO) on the rheological properties of the lignin adsorption layer at the decane-water interface.

FIG. 3 shows the kinetics of adsorption kinetics of lignin at the decane-water interface with and without nanoparticles. From the results obtained, it is found that in the presence of ZnO, the decane-water surface tension is the lowest, whereas with TiO 2 (Eusolex TS) and TiO 2 (Eusolex T2000), the surface properties of the lignin are diminished. TiO2 W877, on the other hand, slightly favors the surface properties of lignin.

The effect of the presence of ZnO and TiO 2 nanoparticles on the physicochemical properties of the lignin adsorption layer at the decane / water interface were collated in the following Table 4:

Table 4

Thus, it is clear that the ZnO nanoparticles increase the expansion modulus of the lignin adsorption layer.

Example 5. Measurement of anti-UV capacities (SPF test) of decane / stabilized water emulsions with different lignin concentrations and variable lignin / T1O2 particle ratios

Different samples were tested. The control sample is a formulation outside the invention, comprising 2% of T1O2 nanoparticles, allowing a comparison of the properties of emulsions 1, 2 and 3 according to the invention. The density of decane is 0.726 g / cm 3 at 25 ° C., which makes it possible to calculate its percentage by weight in the emulsion.

Table 5

The sun protection factor (SPF) and the UVA protection factor measurements are carried out according to conventional techniques well known to those skilled in the art.

Table 6

It appears that the best SPF is obtained when the concentration of TiC> 2 is the most important (2%) in the control sample. Nevertheless, and surprisingly, it is observed that the decrease in the TiO 2 level is not accompanied by a similar decrease in the UV protection; indeed: - sample 1 comprises 0.6% of TiO 2, 3.3 times less than in the control sample: nevertheless, the SPF is decreased by only 1.678 times, and the FP-UVA by 1.515 times;

sample 3 comprises a very low dose of TiO 2: 16.66 times less than in the control sample; nevertheless, the SPF is decreased by only 2.35 times and the FP-UVA by 2.079 times.

Figure 4 illustrates this moderate increase in SPF and FP-UVA as a function of the concentration of TiO 2 nanoparticles.

Thus, the combination of nanoparticles of titanium dioxide with lignin makes it possible to limit the quantity of nanoparticles used, while maintaining a sun protection factor (SPF) and a protection factor against UVA sufficient for the protection of the active compounds lipophilic.

BIBLIOGRAPHIC REFERENCES EP 018772 WO 2012/156652 US 2002/0182155 C. Pouteau, P. Dole, B. Cathala, L. Averous, N. Boquillon. Antioxidant Properties of Lignin in Polypropylene, Polymer Degradation and Stability; 81 (2003) 9-18.

Rojas Orlando .; Johnny Bullon; Ysambertt Fredy; Forgiarini Ana; Salager Jean-L .; Argyropoulos Dimitris. Lignins have emulsion stabilizers. ACS Symposium Series, 2007, Vol. 954, pp. 182-199. H Shi, R Magay, V Castranova, J Zhao: Titanium dioxide nanoparticles: a review of current toxicological data. Particle and Fiber Toxicology 2013 10:15

Report adopted by the Cosmetology Commission of March 15, 2011 (AFSSAPS). State of knowledge of nanoparticles of titanium dioxide and zinc oxide in cosmetics in terms of skin penetration, genotoxicity and carcinogenesis. Referral 2008 BCT0001 B. Worlds. "Preparation of dioxane lignin fractions by acidolysis" Methods in Enzymology 161 (1988): 31-35.

Claims (10)

An "oil-in-water" type emulsion comprising an aqueous phase, a fatty phase, and an adsorption layer at the interface of the two phases, said adsorption layer consisting of a lignin matrix in which are incorporated metal oxide nanoparticles, characterized in that the lignin is present in an amount of less than 2% by weight, and that the metal oxide nanoparticles are present in an amount of less than 1.5% by weight, relative to total weight of the emulsion. 2. Emulsion according to claim 1, characterized in that the metal oxide nanoparticles are zinc monoxide particles or titanium dioxide particles. 3. Emulsion according to claim 1 or 2, characterized in that the metal oxide nanoparticles are bonded to the lignin matrix by non-covalent bonds. 4. Emulsion according to one of claims 1 to 3, characterized in that the metal oxide nanoparticles are incorporated into the lignin matrix by sonication. 5. Emulsion according to claim 1 or 2, characterized in that the metal oxide nanoparticles are bonded to the lignin matrix by covalent bonds. 6. Emulsion according to one of claims 1 to 5, characterized in that the nanoparticles of metal oxide are present in a ratio by weight nanoparticles / lignin between 0.1 and 0.8, and more preferably are present in a ratio by weight nanoparticles / lignin about 0.5. 7. Emulsion according to one of claims 1 to 6, characterized in that the lignin is of natural origin. 8. Emulsion according to claim 7, characterized in that the lignin is derived from a process for extracting cellulose from plants. 9. Emulsion according to one of claims 1 to 6, characterized in that the lignin is of synthetic origin. 10. Emulsion according to one of claims 1 to 9, characterized in that the fatty phase comprises an organic solvent selected from cyclopentane, hexane, methylcyclohexane, heptane, decane, dodecane and toluene.